Restricted Earth Fault Protection Testing

Restricted Earth Fault Protection Testing

Restricted Earth Fault Protection Testing Services:

  • Secondary Injection Testing
  • CT Analysis
  • NEE Point Testing
  • Polarity Testing

Restricted earth fault protection is provided in HV transformers to protect the transformer low voltage winding. The CT secondary of each phase are connected together.

Then common terminals are connected to the Neutral CT. Whenever there is an unbalance in between three phases of the power transformer, a resultant unbalance current flow through the Neutral CT.

In a Restricted Earth Fault scheme the common terminals of phase CTs are connected to the secondary of Neutral CT in such a manner that secondary unbalance current of phase CTs and the secondary current of Neutral CT will oppose each other.

If both electric currents are equal in amplitude there will not be any resultant current circulating in the secondary cabling through the relay.
Hence the relay will not respond even there is an unbalancing in phase current of the power transformer.

For more information about how C&P can help with your Restricted Earth Fault Protection Testing, please call 01792 897002 or email

For further information about C&P’s High Voltage and other Integrated Electrical Services, please click on one of the links below: